Tall fescue is a hardy, rangeland grass, which is a primary forage for grazing ruminants, especially during the hot summer months. It is grown on approximately 1.4 million hectares throughout the United States. The ability of tall fescue to withstand temperature extremes is, at least in part, a result of a symbiotic relationship between the plant and an endophytic fungus, Neotyphodium coenophialum. It is estimated that greater than 80% of all fescue is infected with the fungus.
Although the symbiosis has advantages for the grass, N. coenophialum also produces ergovaline and ergot alkaloids. These naturally occurring chemicals are responsible for fescue toxicosis, a widespread problem affecting both beef and dairy cattle. Data indicates that feeding ruminants ergovaline impairs their performance (Gadberry M. S., Denard T. M., Spiers D. E., Piper E. L., “Effects of feeding ergovaline on lamb performance in a heat stress environment,” J. Anim. Sci. 2003 June; 81(6):1538-45). Conversion of ergovaline to ergot alkaloids leads to detectable concentrations of alkaloids in the urine, which are correlated with toxicosis symptoms (Hill N. S., Thompson F. N., Stuedemann J. A., Dawe D. L., Hiatt E. E., “Urinary alkaloid extraction as a diagnostic tool for fescue toxicosis in cattle,” J. Vet. Diagn. Invest. 2000 May; 12(3):210-7). Absorbed ergovaline and ergot alkaloids cause a reduction in vasoactivity (Oliver J. W., Abney L. K., Strickland J. R., Linnabary R. D., “Vasoconstriction in bovine vasculature induced by the tall fescue alkaloid lysergamide,” J. Anim. Sci. 1993 October; 71(10):2708-13) and subsequent impairment of heat regulation. Impairment of immune function also is observed. Cattle affected by fescue toxicosis suffer from reduced appetite and growth, impaired reproduction and lactation, and impaired circulation to the extremities, which leads to the inability to dissipate heat during summer heat stress or, in winter, the inability to maintain circulation to the feet and tail. Often tails will turn gangrenous and fall off. In more severe situations, feet also will be affected and lost.
Currently, no dietary intervention is available to effectively prevent or treat fescue toxicosis. Methods such as ammoniation of feedstuffs (Simeone A., Boissonneault G. A., Bush L. P., Mitchell, Jr., G. E., “Comparison of two ammoniation procedures to reduce the toxicity of endophyte-infected tall fescue seed fed to rats,” Drug Chem. Toxicol. 1998 August; 21 (3):387-404) require additional handling and expense and are not applicable to grazing situations where fescue toxicosis is predominantly observed. The use of vaccines (Filipov N. M., Thompson F. N., Hill N. S., Dawe D. L., Stuedemann J. A., Price J. C., Smith C. K., “Vaccination against ergot alkaloids and the effect of endophyte-infected fescue seed-based diets on rabbits,” J. Anim. Sci. 1998 September; 76(9):2456-63) or dopamine antagonists (Samford-Grigsby M. D., Larson B. T., Forcherio J. C., Lucas D. M., Paterson J. A., Kerley M. S., “Injection of a dopamine antagonist into Holstein steers to relieve symptoms of fescue toxicosis,” J. Anim. Sci. 1997 April; 75(4):1026-31) require multiple injections of pharmacological materials which are expensive. Injections lead to high labor and animal handling requirements and place additional stress on animals.
Combinations of mineral clay and yeast cell wall extracts have been used to bind and inactivate ergot alkaloids when admixed with feeds or fed directly to animals (U.S. Pat. No. 6,344,221 B1). Calcined aftapulgite clay (U.S. Pat. No. 5,935,623) or a combination of mineral clay and modified yeast wall extracts (U.S. Pat. No. 6,045,834) have been used to remove mycotoxins from animal feeds. While these compositions and methods may help prevent the introduction of ergot alkaloids into the system of the animal, they do not treat the symptoms of fescue toxicosis such as impaired thermoregulation and impaired immune response that result from absorption of ergovaline and ergot alkaloids.
Thus, feed compositions that limit absorption of ergot alkaloids in digestive systems and/or treat the symptoms of fescue toxicosis in fescue-consuming animals would be of value. Low-cost and non-stressful methods to improve the health and performance of animals consuming endophyte-infected fescue also would be advantageous.